This invention relates to a cylinder identification apparatus for a multi-cylinder internal combustion engine.
As automobile engine make increasing use of electronic control systems, it becomes possible to perform individual control of each cylinder of the engine. In order to carry out individual cylinder control, it is necessary to be able to identify the operating state of each cylinder at any give time. Cylinder identification apparatuses have been developed for carrying out this identification.
A typical cylinder identification apparatus employs sensors for sensing the rotation of some portion of the engine rotating at half the speed of the crankshaft, such as the camshaft or the distributor shaft. One type of conventional cylinder identification apparatus comprises a rotating disk having a plurality of circumferentially-extending slots formed therein, each of the slots corresponding to one of the cylinder of the engine. A light-emitting element and a photoelectric element are disposed on opposite sides of the rotating disk. Each time one of the slots in the disk passes between the light-emitting element and the photoelectric element, the photoelectric element generates an electrical output signal which is used as a cylinder identification signal. Each of the slots has a different circumferential length, so the pulse width of the cylinder identification signal is different for each slot. Therefore, by measuring the pulse width of the cylinder identification signal, it can be determined which cylinder is indicated by a given pulse of the cylinder identification signal. Each of the pulses of the cylinder identification signal occurs at a prescribed crankshaft angle of the engine, so the cylinder identification signal can also be used as a timing signal for controlling the timing of fuel injection and ignition.
While a conventional cylinder identification apparatus is able to perform accurate cylinder identification, it has the problem that the relationship between the timing of the cylinder identification signal and the crankshaft angle of the engine can vary. This is because the rotating shaft on which the rotating disk is mounted is mechanically connected to the crankshaft by belts or gears which can undergo slippage, and therefore a phase difference can develop between the actual crankshaft angle and the crankshaft angle indicated by the cylinder identification signal. When such a phase difference develops, it is impossible to accurately control the timing of ignition and fuel injection on the basis of the cylinder identification signal.